when i am looking at my photos the beach ball comes up and it slows down the scrolling... should i rebuild the database?

is a good idea to rebuild database in iphoto when is acting slow, every time i scrolled up or down the beach ball shows up?

When did this start? After you imported new photos? Then you may have imported a photo or video that cannot be processed. You may want to check the Console window, if you are seeing error messages or diagnostic messages when you are scrolling. The Console application can be launced from Applications > Utililities.

Slowness can also be a problem because of an overfull system drive. Check, how much free disk space you are having. If you are getting close to only 10 GB free space on your System drive, it will be high time to empty the trash and to free more disk space.

In all other cases it s a very good idea to start truble shooting by repairing your iPhoto library, and if that does not help, to rebuild it, after backing up the library.

Added:

Before you rebuild, check, if you have the same problem with a new library. Create a new test library, import a few photos, and test. Is iPhoto also unresponsive?